Technical Aspects of Digital Cameras

• Plane of Focus: The 2-dimensional area of focus within the scene. It is parallel to the sensor plane and at the same distance from the lens as the focal point.
• Sensor Plane: The surface onto which the image is projected and recorded.
• Focal Length: The distance in millimeters (mm) from the optical center of a lens to its point of focus at the sensor plane when focused at infinity. A normal focal length lens (typically 50mm on a full frame sensor) recreates the field of view of the human eye. A shorter focal length lens (wide-angle) captures a wider field of view. A longer focal length lens (telephoto) captures a narrower field of view. A prime lens has a fixed focal length, while a zoom lens encompasses a range of focal lengths. Focal length also affects the spatial relationships within the scene, as shorter focal lengths exaggerate distance making items seem further apart, while longer focal lengths compress distance causing items to appear closer together than they may be.

Figure 6. Illustration of plane of focus, focal length, and sensor plane.
(Image Credit: SWGDE, 2025)

• • Focus: The point where light rays reflecting from the object converge. Below are some examples of common camera focus modes:
  • Auto: The camera chooses the focus point(s) used to obtain focus. Typically, the closest subject is chosen by default.
  • Single Point: The user chooses the focus point to be used, and the camera only uses that point to obtain focus. Useful for small or immobile subjects.
  • Group: The user selects a predetermined grouping of focus points to obtain focus. Useful for larger subjects.
  • Continuous: The camera continually refocuses at a given focus point(s) as long as the shutter button is partially depressed. Useful for moving subjects.

• White Balance: A camera setting that adjusts the color temperature of an image to ensure that colors are reproduced accurately, regardless of the lighting conditions. Different light sources have different color temperatures, measured in Kelvin (K) (Figure 7).

The white balance setting must be calibrated to the light source(s) being used. Different white balance settings include Tungsten, Fluorescent, Daylight, Cloudy, Shade, Flash, and Auto White Balance (Figure 8). If the lighting conditions are a mixture of different color temperatures, a custom white balance may be necessary.

Figure 7. Example of different color temperature settings.
(Image Credit: SWGDE, 2025)

Figure 8. The effects of white balance on colors in an image.
(Image Credit: SWGDE, 2025)

• Depth of Field: The area in front of and behind the plane of focus (1) that is in acceptably sharp focus within an image (2). The aperture controls the depth of field. A smaller aperture, represented by a higher f-number results in a greater depth of field (Figure 9a), and a larger aperture, represented by a smaller f-number results in a shallower depth of field (Figure 9b). The depth of field extends approximately ⅓ in front and ⅔ behind the plane of focus. Lens focal length and camera to subject distance will also have an effect on depth of field.

Figure 9. Depth of Field.

(Image Credit: MikeRun, Wikimedia Commons, 2019 [6]MikeRun “File: Depth-of-field.svg.” Wikimedia Commons, 28 Dec. 2019, https://commons.wikimedia.org/wiki/File:Depth-of-field.svg. Accessed 14 Jan. 2025.)

• Exposure Compensation: Purposely creating a darker or lighter exposure, based on the conditions of the scene. This is accomplished via an exposure compensation setting on the camera where the amount of over or under-exposure can be adjusted as needed.
• Bracketing: The process of taking the same picture multiple times using different camera settings resulting in differing exposures. This can be performed manually or by engaging the bracketing feature in the camera. Doing so will purposely take a series of photos at a range of exposure levels, from underexposed to overexposed.

Figure 10. An example of bracketing or exposure compensation.
(Photo Credit: SWGDE, 2025)

• Metering Mode: The camera will use one of several light metering modes to measure the light values in a scene and determine proper exposure. These modes dictate what part of the frame is evaluated. Different light metering modes help the photographer control the exposure depending on the desired result. Below are some examples of common light metering modes:
  • Spot: A small, predetermined area of the frame is used to measure light values.
  • Center Weighted: The center area of the frame is given priority to measure light values.
  • Matrix / Evaluative / Multi: The entire frame is used to measure light values.